This invention relates to the manufacture of semiconductor devices and more particularly to a process incorporating temperature gradient zone melting techniques.
Temperature gradient zone melting is a process in which a small amount of a migrating material is placed on the surface of a larger body of a carrier material and the combination is raised to an elevated temperature. A temperature gradient is imposed across the body of carrier material with the migrating material at the cool end. A melt containing both of the materials is formed and migrates toward the hotter portion of the carrier material. In the path of the melt is left a recrystallized region of the carrier material containing a concentration of the migrating material in an amount equal to the solid solubility limit at the temperature of migration. This process has been found useful in the manufacture of semiconductors. When used in semiconductor manufacture, the carrier material is typically a body or wafer of semiconductor material such as silicon, germanium or a compound semiconductor material such as gallium arsenide. The migrating material is generally a conductivity modifying impurity such as aluminum, but it can serve other purposes, such as altering carrier lifetime if gold or platinum is migrated.
When practicing temperature gradient zone melting in the manufacture of semiconductor devices, it was occasionally found that processes requiring post TGZM masking and etching operations provided an unexpectedly low yield. It was discovered that this was due to a difficulty in effectively masking the wafer caused by irregularities in the surface formed during the temperature gradient zone melting process.
It is an object of this invention, therefore, to provide a technique which overcomes the aforementioned disadvantages when temperature gradient zone melting is used in the manufacture of semiconductors.